Coating polyethylene with haloethylene polymers and composite articles thereby obtained



July 28, 1959 D. G. GRENLEY ET AL 2,897,100

' OOATING POLYETHYLENE WITH HALOETHYLENE POLYMERS AND Y COMPOSITE ARTICLES THEREBY OBTAINED Filed Dec. 5, 1956 v Pre/caring acca/ing compos/'han coms/.s/'ng of a /afex emu/Jion of a ha/oe//zy/ene polymer res/'n by incorpora/ing in he Jafex a m/norproper/fon o/a Sur/ace acf/'ve sod/'um 'sa/f of condensed ary/su/fon/'c acids '/oo/ye/ecro/y/e 1N V EN TORS. 00//06 6. Gren/ey Hara/afd Townsend TTOR/VEYS 2 Sheets-Sheet 2 M United States Patent() COATING POLYETHYLENE WITH HALOETI-IY-r- POLYMERS AND COMPOSITE ARTICLES THEREBY OBTAINED Application December 3, 195:6SerialANo. '625,938 16 Claims. (Cl. 1117'138.8)

This invention relates to a method for coating polyethylene iilms and other shaped articles with resinous layers comprised `of haloethylene polymers and copolymers and to the coated articles, particularly films, which may thereby be obtained. v

Films `and other shaped and molded articles of polyethylene have many attractive characteristics including, in general, good physical properties and, in particular, excellent behavior and resistance to embrittlement at low temperatures. The latter feature is not readily obtainable in articles which are comprised of haloethylene polymers and haloethylene polymer resins which mayconsist of various polymers and copolymers of vinyl halides and of vinylidene halides including, especially, copolymers of vinylidene chloride and vinyl chloride and, copolymers of vinylidene chloride and acrylonitrile, which vinylidene halide copolymers frequently are generically described as being sarans. On the other hand, lm structures and other shaped articles and coatings prepared from haloethylene polymer resins and particularly from sarans have an outstandingability to provide particularly effective barriers against the-transmission or permeation of gases or vapors. Furthermore, haloethylene polymer resins are usually not as prone to becoming surface scuifed or marred in use asV are the typical polymersof ethylene.

Despite the obvious beneficial utility as aflexible, vaporproof lm article or other container which would be especially well suited for low temperature employment that could be provided by composite structures comprised of polyethylene film or other shaped or molded articles coated with or laminated to haloethylene polymer resin compositions, much difliculty has been experienced in their derivation. This is because of the inefficient bonding and poor adherence that is experienced when haloethylene polymer resin coatings or laminating lms are attempted to be formed into composite structures with polyethylene articles. Polyethylene iilm and otherarticles, as is well known, commonly have a smooth and sleek, relatively slippery and Wax-like surface which is poorly adapted to provide for suitable adhesion or anchorage of applied materials by mere physical attachment. Furthermore, the relatively inert chemical nature of polyethylene resists the eicient attachment of most materials lby chemical interlinkage or bonding.

It is among the principal objects of the present invention to provide an eicient and effective method for coating polyethylene lrns and other articles with tightlyadhering integral layers of haloethylene polymer resin compositions including, in particular, saran compositions. It is also an object of the invention to provide utile composite structures of polyethylene lms and articles and haloethylene polymer resin coatings on the articles which are particularly adapted for employment at relatively low temperatures as exible, vapor-proof materials for packaging and the like. Other objects and advantages will be apparent in the following description and specication.

According to the invention, polyethylene articles mayA ice may beetfectively providedvvith a tightly-adhering and rmly anchored coating of a haloethylene polymer resin by a method which comprises incorporating a minor l'proportion of a surface active polyelectrolyte material that contains a plurality of ionizable groups in its molecule and is of the general class that may be delineated as being a neutral sodium salt of a condensed arylsulfonic acid selected from the group of such surface active materials which consists of those popularly known as Tamol X, Tamol N and mixtures thereof, in a coating compositionconsisting of a latex emulsionA of said haloethylene polymer resin; applying a layer of the latex emulsion of the haloethylene polymer resin in which is incorporated said surface active material over the polyethylene surface; and subsequently drying the applied latex emulsion of the haloethylene polymer resin to eifect a solid deposition of resin on the surface of the polyethylene.

The composite articles (as illustrated by the composite iilm which is depicted perspectively in Figure 1 and cross-sectionally in Figure 2 and by the internally coated tubular article shown` perspectively in Figure 3 of the accompanying drawing), lwhich advantageously may be obtained by practice of the present invention, possess to an unusual degree many of the desirable and benecial attributes `and properties of both polyethylene and haloethylene polymer resins. They are quite Vpliable while being strong, tough and tear resistant and retain their strength and flexibility at relatively lowtempera'- tures. They have a more scuif-resstant and harder-tomar surface than plain polyethylene and are extremely impermeable to gases and vapors. The composite articles are possessed of a nstrong and effective bond between the applied coating of haloethylene polymer resin and the coatedpolyethylene article. Figure 4 of the accompanying drawing schematically illustrates the present method in the manner of a llow sheet diagram.

In most instances, the applied coating is extremely diiiicult if not completely impossible to strip from the surface of the polyethylene film or otherv article by ordinary physical methods. In addition, such composite structures have an unusual transparency and freedom from haze when they are in relatively thin sections in comparison with conventional polyethylene lm and other thin articles. For example, composite film structures in accordance with the invention may generally be obtained with only a very slight degree of haziness which is not discernible upon ordinary visual inspection and which has been reduced almost to the vanishing point from the haze that is present in the original polyethylene lm. y

Composite lm structures may advantageously be prepared in accordance with the present invention. Such iilm structures have particular utility as 'Wrapping and packaging materials for foodstuffs and other articles which are intended to be handled or maintained and stored at relatively low temperatures in a refrigerated or frozen condition. Besides providing protection as a strong and tough flexible covering, they also more eifectively prevent the dehydration of the packaged articles and avoid development of the condition known as freezer burn which frequently occurs in inadequately protected frozen foods. Other composite structures including tubes, exible bottles and other containers such as cartons and boxes may also be made with advantage by practice of the invention.

Advantageously, relatively thin polyethylene iilms are employed `in order to obtain composite film structures according to the invention. Beneiicialresults, forexample, are readily obtainable with ilms having a thickness which is not greatly in excess of about 20 mils. )It

is frequently even more benecial to employ polyethylene vlilms that have a thickness between about 0.5 and 5.0 mils. The polyethylene lrn which is employed in the practice of the present invention as Well as other polyethylene articles may be derived from polyethylene of any nature. The polymers of ethylene which are employed may, for example, be similar to those which sometimes are referred to as polythenes and which may be obtained by polymerizing ethylene in a basic aqueous medium and in the presence of polymerization-favoring quantities of oxygen under relatively high pressures in excess of 500 or 1,000 atmospheres at temperatures which may be between 150 and 275 C. Or, if desired, they may be similar to the essentially linear and unbranched polymers which have been referred to as ultrathenes and which ordinarily have greater apparent molecular weights (as may be determined from such characteristics a's'their melt viscosities and the like) in excess of at least about 20,000 and generally in excess of about 40,000; densities of about 0.94-0.96 gram per cubic centimeter; and melting points in the neighborhood of 12S-135 C. They are ordinarily found to have a more crystalline nature than conventional polyethylenes and may contain less than 3.0 and even less than 0.3 methyl radical per 100 methylene groups in the polymer molecule. The essentially linear and unbranched polymers of ethylene may be obtained under relatively low pressures of 1 to 100 atmospheres using such catalysts for polymerizing the vethylene as mixtures of strong reducing agents and compounds of group IV-B, V-B and VI-B metals of the periodic system; chromium oxide on silicated alumina; hexavalent molybdenum compounds; and charcoal supported nickel-cobalt.

The haloethylene polymer resin employed in the latex emulsion for coating the polyethylene surface may advantageously be a saran copolymer suchv as a copolymer of vinylidene chloride and vinyl chloride or a copolymer of vinylidene chloride and acrylonitrile or a copolymer or vinylidene chloride and acrylic acid or its ester derivatives. iff desired, however, the haloethylene polymer resin that is utilized in the coating latex emulsion may be polyvinylchloride or a copolymer of vinyl chloride and vinyl acetate that contains at least about 80 percent by weight of vinyl chloride polymerized in the coplymer molecule. It is particularly advantageous to employ crystalline saran copolymers in the latex emulsions to be coated on the polyethylene surfaces and even more adv antageous in many instances to utilize such copolymers of vinyl chloride and vinylidene chloride as may contain at least about 80 percent by Weight of vinylidene chloride polymerized in the copolymer molecule or such copolymers of vinylidene chloride and acrylonitrile as may contain atleast about 60 and, preferably, from 85 to 95 percent by weight of vinylidene chloride polymerized in the copolymer molecule.

The surface active polyelectrolyte materials that are employed in the practice of the invention and which are of the. general class of such materials that may be dened as being neutral Water soluble sodium salts of arylsulfonic acids which have been condensed (generally with formaldehyde or an equivalent condensing agent) are thought, upon the basis of reasonable information and belief, to be a product of the general type that has been disclosed and is covered in United States Letters Patent Nos. 1,232,620; 1,237,405; 1,281,494 and 1,336,759. As has been indicated, they are the type of materials that are popularly referred to and known as being Tamol X and Tamol N which are the trade-designations under `which they are available from Rohm & Haas Company of Philadelphia, Pennsylvania. Surprising as Ait may "seem, the utilization of Tamol X or Tamol N, or both, provides superlative results and secures to a marked extent'the purposes that ane'intended to be vaccomplished by the invention'while an 'exactly similar use vof many -othe'rsurface active materials, as is hereinafter demonstrated, does not significantly afect or inliuence the adhesion of the halo-ethylene polymer coating composition to the polyethylene surface. This is so even when surface active materials that have a remarkable ostensible similarity to Tamol X or Tamol N are involved.

Between about 0.1 and 5.0 percent by weight of the indicated type of surface active material, based on the weight of the haloethylene polymer resin in the latex emulsion coating composition, may advantageously be incorporated in the latex emulsion coating composition to ameloriate its adherence and bonding to the surface of the polyethylene to b e coated. -In many instances it may be more advantageous to employ an amount of the surface active material that is between about 0.5 to 3.0 percent by weight of the polymer solids. The surface active additament is usually best b'dmectly incorporated as a relatively concentrated aqueous solution in the latex emulsion coating composition. In this connection, the surface activematerial may frequently be beneficially employed as the emulsion stabilizer for the haloethylene polymer latex coatingv composition.

In order to secure better adhesion of the coating latex emulsion compositions, it maybe beneficial to utilize a flame treatment or the like on the uncoatedv surface of the polyethylene to augment its wettability. The coating may be accomplished by variousspread, dip, brush, spray-or other casting techniques.

Advantageously, the composite lm structures may be suitably formed by spread coating a latex preparation having in the neighborhood of 50 percent by weight of the haloethylene polymer resin solids that, as has been mentioned, contains the incorporated surface active material as an emulsiier for the system. After application, the surface active material-containing haloethylene polyiner resin latex emulsion compositions may be dried according to usual and conventional techniques to eect a solid deposition of the tightly-adhering resin layer in the composite structure. The particular drying conditions that are required (insofar as whether room temperatures or heat at elevated temperatures is necessary'to lbest dry the applied latex emulsion) depends, as will be apparent to those skilled in the art, to a great extent upon the characteristics of the particular haloethylene polymer resin that is involved.

The pHL of the latex coating composition may have to be adjusted to avoid undesired coagulation while accommodating the incorporated surface active material. While different thicknesses may also be beneficial, it is desirable for the applied and finally dried layer of haloethylene polymer resin on the surface of the polyethylene article to be at least about 0.02 mil thick and even more desirable for it to have a thickness between 0.1 and 2.0 mils. As is apparent, films may, if desired, be coated on both of their surfaces in accordance with the invention. In a similar manner, all of the coatable surfaces of other articles such as both of the inner and outer surfaces of containers and the like or either surface or any desired 'portion of a particular surface may, as desired, be providedr with the polyelectrolyte-containing haloethylene polymer resin coating.

By VWay of further illustration a number of polyethylene lms were coated to a 0.10 mil thickness with a saran polymer resin that consisted of a copolymer of acrylonitrile yand vinylidene chloride containing about 89 percent by weight of vinylidene chloride polymerized in the copolymer molecule. The coatings were applied by conventional spread techniques from various vlatex formulations containing about 50 percent by weight of polymeric solids in which dilferent surface active materials were incorporated. The polyethylene lm which was employed had a thickness of about 1 mil and was of thetypewhich isknown as Dura-Clear polyethylene lm and which is obtainable from The Harwid Company of Boston, VMassachusetts. After the coatings had dried fon the ypolyethylene "film samples, 'the composite lm structures were tested for the adhesive properties of the applied coatings on the lm at room temperature by determining the force in grams that was necessary to strip or peel a '3A inch wide layer of the coating from the film. The results are given in the following tabulation in which the surface active agents that were incorporated in each of the coating formulations are identitled and which includes the quantities of the surface active agent that were employed.

2. The method of claim 1, wherein between about 0.1 and 5 percent by weight of the surface active polyelectrolyte material is incorporated in the coating composition, based on the weight of the haloethylene polymer resin contained therein.

3. The method of claim l, wherein between about 0.5 and 3 percent by weight of the surface active polyelectrolyte material is incorporated in the coating composition,

Quantity of surface active Force in Trade designaagent gms. necestion of surface employed sary to active agent Type of material Available fromin perpeel employed in cent by strip. of termination weight, applied based on coating polymer solids Po1yg1ycc131 Butyl phenol monoether of a polyethylene glycol The DOW Chemical Oo 3 125 Triton Xl00 Alkyl aryl polyether alcohol R0hm- & HMS 00 3 115 Aertol MA Dihxyl ester of sodium sulfosuccinic aeid Amllcll cya-Hamid CO- :'13 (g5 o o 0 5 Victawet 58B- Na5(capryl)5(PaO10)g Victor Chemical Works 3 33 Igepal OA Alkyl phenoxy polyoxyethylene ethanol. Antara Chemicals Div. of General 3 40 Dyestuis Corp. Ultrawet DS. Alkyl benzene sodium sulfonate Atlantic Refining 00.... 3 40 Daxad 11 Naphthalene suifonic acid Dewey & Almy Chemical Oo 3 About to Daxad 11KLS Lowdsalt concentration potassium salt of alkyl naphthalene SulfOlue -d0 3 About 40 aci Darvan No. 1 Sodium salt oi polymeric alkyl aryl sulfonlc acid (probably fOrmal- R- T. Vanderbilt & C0 3 About 40 dehyde condensation product). n Lomar PW..- Sodium salt of condensed mononaphthylene sulfonic acid Jacques Wolf lz Co 3 About 40 Lemar PWA Ammonium salt of condensed mononaphthylene sulfome ac -d0 3 About 40 Tamol X.-. Neutral sodium salt of condensed arylsulfom'c acid Rohm & Haas Oo-. 3 750 Tamol N do o 3 750 The films coated with the Tamol X and Tamol containing latex formulations had good flexibility and did not become embrittled at temperatures as low as C. In addition, their effectiveness as Water vapor barriers was commensurate to that which is obtainable from conventional saran films. Further, they had excellent clarity and transparency. Their degree of haziness was reduced substantially completely in compason to that which is present in the original polyethylene lms with which they were prepared.

Similar results may be obtained when other proportions of Tamol X and Tamol N or their mixtures within the scope of the invention are incorporated in the latex coating composition and .when compositions of other haloethylene polymer resins are employed. Films of essentially linear and unbranched polyethylene may also be satisfactorily coated in the foregoing manner.

Certain changes and modifications in the practice of the present invention can be readily entered into without departing substantially from its intended spirit and scope. Therefore, it is to be fully understood that the invention is not to be limited or in any way restricted by the preferred embodiments thereof which are set forth in the foregoing description and specication. Rather, it is to be interpreted and construed in the light of what is set forth and detailed in the hereto appended claims.

What is claimed is:

1. Method for coating a polyethylene article with a haloethylene polymer resin which comprises applying, as a coating composition, a layer of a latex emulsion of a haloethylene polymer resin in which there has been incorporated a minor proportion of a surface active polyelectrolyte material over the polyethylene surface, said surface active polyelectrolyte material containing a plurality of ionizable groups in its molecule `which is a watersoluble neutral sodium salt of condensed arylsulfonic acids in a coating composition consisting of a latex emulsion of said haloethylene polymer resin; and subsequently drying the applied latex emulsion of the haloethylene polymer resin to effect a solid deposition of resin on the surface of the polyethylene.

based on the weight of the haloethylene polymer resin contained therein.

4. The method of claim 1, wherein the polyethylene article is a film having a thickness which is not in excess of about 2O mils.

5. The method of claim l, wherein the polyethylene article is a iilm having a thickness which is between about 0.5 and 5 mils.

6. The method of claim 1, wherein the layer of the haloethylene polymer resin which is applied over the surface has a thickness of at least about 0.02 mil.

7. The method of claim l, wherein the layer of the haloethylene polymer resin which is applied over the surface has a thickness of between about 0.1 and 2.0 mils.

8. Composite structure which comprises a polyethylene article coated with a tightly-adhering layer of a haloethylene polymer resin in which there is incorporated a minor proportion of a surface active polyelectrolyte material that contains a plurality of ionizable groups of its molecule, said surface active polyelectrolyte material being a water soluble neutral sodium salt of condensed arylsulfonic acids.

9. The composite structure of claim 8, wherein the ap'- plied coating has a thickness of at least 0.02 mil.

10. The composite structure of claim 8, wherein the applied coating has a thickness between about 0.1 and 2.0 mils.

11. The composite structure of claim 8, wherein the polyethylene article is a lm having a thickness between about 0.5 and 5 mils.

l2. The composite structure of claim 8, wherein the haloethylene polymer contains between about 0.1 and 5.0 percent by weight of the surface active polyelectrolyte material incorporated therein.

13. The composite structure of claim 8, wherein the haloethylene polymer contains between about 0.5 and 3.0 percent by weight of the surface active polyelectrolyte material incorporated therein.

14. The composite structure of claim 8, wherein the haloethylene polymer resin is comprised of a crystalline vinylidine chloride polymer.

15. The composite structure of claim 8, wherein the haloethylenepolymeiresin is comprised of a copolymer which contains acrylonitrile and vinylidene chloride polymerizel-in its molecule.

16. The composite structure of claim 8, wherein the polyethylene article is derived from an essentially linear and .unbranched polyethylene having a molecular Weight in excess of about 40,000; a density between about 0.94 and 0.96 gram per cubic centimeter; and a melting point in the neighborhood of 12S-135 C.

References Cited in rthe file of this patent 

1. METHOD FOR COATING A POLYETHYLENE ARTICLE WITH A HALOETHYLENE POLYMER RESIN WHICH COMPRISES APPLYING, AS A COATING COMPOSITION, A LAYER OF A LATEX EMULSION OF A HALOETHYLENE POLYMER RESIN IN WHICH THERE HAS BEEN INCORPORATED A MINOR PROPORTION OF A SURFACE ACTIVE POLYELECTROLYTE MATERIAL OVER THE POLYETHYLENE SURFACE, SAID SURFACE ACTIVE POLYELECTROYLTE MATERIAL CONTAINING PLURALITY OF IONIZABLE GROUPS IN ITS MOLECULE WHICH IS A WATERSOLUBLE NEUTRAL SODIUM SALT OF CONDENSED ARYLSULFONIC ACIDS IN A COATING COMPOSITION CONSISTING OF A LATEX EMULSION OF SAID HALOETHYLENE POLYMER RESIN; AND SUBSEQUENTLY DRYING THE APPLIED LATEX EMULSION OF THE HALOETHYLENE POLYMER RESIN TO EFFECT A SOLID DEPOSITION OF RESIN ON THE SURFACE OF THE POLYETHYLENE. 